208 VEGETABLE SUBSTANCES. 



This mixture is well agitated every day for a fort- 

 night; it is then allowed to subside for a day or two, 

 after which it is poured into shallow vessels, and 

 half a pint of spirits of turpentine is put to each 

 gallon of oil. After three days' exposure to the heat 

 of the sun it becomes as white as nut oil. 



Linseed, before it is submitted to the mill, is 

 sometimes subjected to the action of heat, for the 

 purpose of getting rid of the mucilage which resides 

 in the brown husk of the seed, arid which absorbs a 

 large proportion of the oil as it is forced out of the 

 kernel. To this end it is placed in a large iron 

 vessel shaped like a sand-bath, and fixed in a fur- 

 nace ; a moderate heat is applied, and the seed is con- 

 stantly stirred that all may alike be roasted ; but 

 there is much hazard of burning some part, thus 

 injuring the oil in the kernel, and giving it a greater 

 tendency to rancidity. A larger quantity is, how- 

 ever, obtained in this manner. 



HEMP OIL. 



Hemp-seed likewise affords a very useful oil, 

 similar in its qualities to linseed. It is of a green 

 colour, and strongly impregnated with the peculiar 

 odour of the plant. 



In Russia this oil is produced abundantly from 

 the vast quantity of hemp-seed obtained by the 

 extensive cultivation of the plant for other pur- 

 poses. From St. Petersburgh alone 150,000 pood 

 (5,454,545 English avoirdupoise pounds) of hemp 

 oil are annually exported*. 



The boors for the most part extract the oil from 



the seeds themselves by means of little mills, in 



which the seeds are crushed by a small block-pestle 



worked by a horse. After being crushed, they are 



* Tooke's View of the Russian Empire, vol. iii. 



